The Study On Opto-electrical Properties Of Random Polymerized Naphathalene Diimde Systems

As the organic electronic devices developing towards multifunctional integration,organic semiconducting materials bearing both the characteristics of solid-state fluorescence and field effect have attracted wide attention in recent years.However,materials with high mobility tend to have a good intermolecularπ-πstacking,and this kind of packing geometry often cause quenching of solid-state emission.In the previous study of our research group,a conjugated polymer PNV has been constructed from a naphthalene diimide（NDI）molecule and a vinyl linker,which exhibits strong red fluorescence in the solid state,with a photoluminescence yield of 33.4%.At the same time,PNV shows n-type field effect properties,but its electron mobility is still at a relatively low level.In this work,a’crystalline modulation strategy‘for constructing such dual functional materials is proposed.The core concept is to adjust the crystalline and amorphous phase in the polymer thin film by introducing functional groups using random polymerization,and thus balance the solid fluorescence and charge carrier mobility of the materials.The detailed contents are as follows:（1）PNV embedded with dithiophene unit:four randomized polymers,PNV-DT1,PNV-DT3,PNV-DT5 and PNV-DT7 based on vinyl flanked NDI incorporating up to7%amount of dithophene,were synthesized.Those polymers exhibited obviously enhanced charge transport ability along the rising dithiophene ratio,whereas their solid emission gradually red shifted towards near-infrared region with bearable PL efficiency loss.Among those polymers,the highest n-type OFETs performance with electron mobility up to 0.011 cm² V^-1s^-1 was achieved from devices based on PNV-DT7,which also exhibited rare near-infrared solid emission at 730 nm induced by the intermolecular charge transfer effect,with considerably strong PL efficiency of 11.2%.GIXRD and AFM analysis manifested that the introduction of dithiophene under such limited ratio could enhance the localizedπ-πintermolecular interaction while retain the overall low crystallized thin film for these polymers,and therefore balance the charge carrier mobility and the solid emission.（2）PNV embedded with DPP unit:six randomized polymers,PNV-DPP0.5,PNV-DPP1,PNV-DPP3,PNV-DPP5,PNV-DPP7 and PNV-DPP10 based on vinyl flanked NDI incorporating up to 7%amount of DPP,were synthesized.The fluorescence of these polymers at 556 nm and 623 nm in the solution and film both decreased with the rise of DPP ratio,indicating that the introduction of DPP resulted in quenching of fluorescence,and the loss of PL efficiency excessed our acceptable range.We speculate that the planar structure of DPP further improves the co-planarity of the polymer backbone,and as it forms localized D-A structure with NDI,it reduces the band gap,facilitates the charge transfer within the molecule,and enhances the localized interaction between molecules,resulting in severe fluorescence quenching.